Peter W. Smith

Bio: Peter W. Smith is an academic researcher from Bell Labs. The author has contributed to research in topics: Laser & Bistability. The author has an hindex of 29, co-authored 75 publications receiving 3411 citations. Previous affiliations of Peter W. Smith include AT&T Corporation & Telcordia Technologies.

Room temperature excitonic nonlinear absorption and refraction in GaAs/AlGaAs multiple quantum well structures

Abstract: We present detailed experimental studies and modeling of the nonlinear absorption and refraction of GaAs/AlGaAs multiple quantum well structures (MQWS) in the small signal regime. Nonlinear absorption and degenerate four-wave mixing in the vicinity of the room temperature exciton resonances are observed and analyzed. Spectra of the real and imaginary parts of the nonlinear cross section as a function of wavelength are obtained, and these are in excellent agreement with experimental data. A simple model for excitonic absorption saturation is proposed; it accounts qualitatively for the very low saturation intensities of room temperature excitons in MQWS.

Large room‐temperature optical nonlinearity in GaAs/Ga1−x AlxAs multiple quantum well structures

Abstract: We report the first measurements of optical absorption saturation in GaAs/GaAlAs multiple quantum well (MQW) structures at room temperature near the heavy hole exciton peak. Linear absorption shows distinct exciton peaks at room temperature in the MQW and we deduce this is because the confinement increases exciton binding energy without increasing LO phonon coupling. This room‐temperature MQW absorption also saturates more readily than that in a comparable GaAs sample; the measured saturation intensity is 580 W/cm2 with a recombination time of 21 ns in a MQW with 102‐A GaAs layers. From this we predict a nonlinear refraction coefficient n2∼2×10−5 cm2/W. This large nonlinearity should permit room‐temperature optical devices compatible with laser diode wavelengths, materials and power levels.

Stabilized, single-frequency output from a long laser cavity

Abstract: The problem of obtaining single-frequency output from a long laser is considered, and two methods are investigated experimentally. The first method consists of using an external filter to select one of a number of oscillating modes. The second method consists of suppressing internally the unwanted resonances so that the laser oscillation can only take place at a single frequency. It is shown that with the second method one can in many cases obtain greater power, and experiments are reported in which single-frequency output power of 15 mW was obtained from a 6328 A He-Ne laser, A simple feedback circuit is described for stabilizing the frequency of the laser oscillation.

Four-wave mixing in an artificial Kerr medium

Abstract: Degenerate four-wave mixing experiments have been performed using a liquid suspension of 0.234-μm-diameter latex spheres as the nonlinear medium. The measured effective optical Kerr coefficient, n2, is 3.6 × 10−3 (MW/cm2)−1. This is ~105× the value for CS2. Measured grating reflectivity, formation, and decay times are in reasonable agreement with a simple model assuming Rayleigh scattering and Brownian diffusion.

Continuous-wave self-focusing and self-trapping of light in artificial Kerr media

Abstract: Artificial Kerr media made from liquid suspensions of submicrometer particles were used as a new type of nonlinear medium for observing cw self-focusing and self-trapping of laser beams. Self-trapping of TEM00-mode beams and higher-order TEM01- and TEM01*-mode beams were investigated. Saturation-free operation down to filament diameters of ~2 μm was observed. The independence of the critical power for self-trapping on the beam diameter in the unsaturated regime was confirmed for the first time to our knowledge. Values of the nonlinear coefficient were determined for a range of particle diameters from 0.038 to 0.234 μm.

Observation of a single-beam gradient force optical trap for dielectric particles

Abstract: Optical trapping of dielectric particles by a single-beam gradient force trap was demonstrated for the first reported time. This confirms the concept of negative light pressure due to the gradient force. Trapping was observed over the entire range of particle size from 10 μm to ~25 nm in water. Use of the new trap extends the size range of macroscopic particles accessible to optical trapping and manipulation well into the Rayleigh size regime. Application of this trapping principle to atom trapping is considered.

Electric field dependence of optical absorption near the band gap of quantum-well structures.

Abstract: We report experiments and theory on the effects of electric fields on the optical absorption near the band edge in GaAs/AlGaAs quantum-well structures. We find distinct physical effects for fields parallel and perpendicular to the quantum-well layers. In both cases, we observe large changes in the absorption near the exciton peaks. In the parallel-field case, the excitons broaden with field, disappearing at fields \ensuremath{\sim}${10}^{4}$ V/cm; this behavior is in qualitative agreement with previous theory and in order-of-magnitude agreement with direct theoretical calculations of field ionization rates reported in this paper. This behavior is also qualitatively similar to that seen with three-dimensional semiconductors. For the perpendicular-field case, we see shifts of the exciton peaks to lower energies by up to 2.5 times the zero-field binding energy with the excitons remaining resolved at up to \ensuremath{\sim}${10}^{5}$ V/cm: This behavior is qualitatively different from that of bulk semiconductors and is explained through a mechanism previously briefly described by us [D. A. B. Miller et al., Phys. Rev. Lett. 53, 2173 (1984)] called the quantum-confined Stark effect. In this mechanism the quantum confinement of carriers inhibits the exciton field ionization. To support this mechanism we present detailed calculations of the shift of exciton peaks including (i) exact solutions for single particles in infinite wells, (ii) tunneling resonance calculations for finite wells, and (iii) variational calculations of exciton binding energy in a field. We also calculate the tunneling lifetimes of particles in the wells to check the inhibition of field ionization. The calculations are performed using both the 85:15 split of band-gap discontinuity between conduction and valence bands and the recently proposed 57:43 split. Although the detailed calculations differ in the two cases, the overall shift of the exciton peaks is not very sensitive to split ratio. We find excellent agreement with experiment with no fitted parameters.

Linear and nonlinear optical properties of semiconductor quantum wells

Abstract: In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Photonic mems and structures

Abstract: An interference modulator (Imod) incorporates anti-reflection coatings and/or micro-fabricated supplemental lighting sources. An efficient drive scheme is provided for matrix addressed arrays of IMods or other micromechanical devices. An improved color scheme provides greater flexibility. Electronic hardware can be field reconfigured to accommodate different display formats and/or application functions. An IMod's electromechanical behavior can be decoupled from its optical behavior. An improved actuation means is provided, some one of which may be hidden from view. An IMod or IMod array is fabricated and used in conjunction with a MEMS switch or switch array. An IMod can be used for optical switching and modulation. Some IMods incorporate 2-D and 3-D photonic structures. A variety of applications for the modulation of light are discussed. A MEMS manufacturing and packaging approach is provided based on a continuous web fed process. IMods can be used as test structures for the evaluation of residual stress in deposited materials.